This invention relates generally to VSB (vestigial sideband) ATSC (Advanced Television Systems Committee) television receivers and particularly to a technique for minimizing viewer inconvenience and data loss due to disturbances, such as airplane flutter and noise, that cause temporary signal impairments.
In the prior art VSB receivers, confidence counters indicate the status of segment sync and frame sync recovery and hence the condition of signal acquisition. In the presence of signal disturbances due to spurious noise, airplane flutter, or the like, the confidence counters indicate a loss of signal condition which results in the resetting of the currently tuned channel, the IF FPLL carrier acquisition loop, the confidence counters and the AGC signal. This results in the receiver initiating a new signal acquisition cycle. The reacquisition procedure takes on the order of 0.1 to 0.3 seconds, during which time the viewing for the user (or the received data) is interrupted. This can be very disconcerting to the user, especially where the signal loss is of very short duration such as that which may occur due to airplane flutter, in which the basic signal is being received in the presence of rapidly changing multipath signals. Upon passage of the signal disturbance, the receiver returns to normal operation with the signal properly locked in.
With the invention, in the event of a signal loss indication, the receiver attempts to quickly reacquire the signal without initiating the relatively long reacquisition process. This is accomplished by resetting only the FPLL IF carrier acquisition loop while maintaining channel tuning and the AGC levels in the tuner and IF blocks. Should the disturbance be short-lived, the FPLL controlling the IF carrier acquisition will quickly relock and the data interruption to the user (or viewer) will be of minimal duration. If the loss of signal indication persists for a longer; predetermined time, then the full signal acquisition procedure is initiated with the currently tuned RF channel, the confidence counters and the AGC being reset along with the IF carrier acquisition FPLL. In this way, the relatively long time to retune the RF channel and stabilize the AGC is eliminated.
A principal object of the invention is to provide an improved VSB television receiver.
Another object of the invention is to provide an enhanced signal reset procedure for a VSB television receiver.
A further object of the invention is to provide a VSB television receiver with enhanced performance under short duration signal loss conditions.